Strategies of air space acquisition in Neotropical savanna trees differing in leaf habit

Context

The Cerrado stricto sensu is a physiognomy under a seasonal climate of Cerrado vegetation, a Neotropical savanna, showing insignificant light restriction for adult tree species with branches above the herbaceous stratum.

Aims

We capture shoot and foliage production in 15 Cerrado tree species with distinct leaf phenology, following marked buds to investigate the strategies of air space acquisition and the influence of monthly air temperature and rainfall over a growing season.

Methods

Five buds were marked in every five individuals per species during the 2016 dry season in deciduous, semideciduous, and evergreen trees, encompassing five species per leaf habit.

Key results

Deciduous trees had plagiotropic shoots with 35° of inclination, whereas semideciduous and evergreen species had orthotropic (60°) shoots. Evergreen Miconia albicans was the single study species with a second-order shoot, and apical meristem death occurred only in deciduous trees. Two deciduous trees (Caryocar brasiliense and Diospyros hispida) and semideciduous Eriotheca gracilipes increased leaf number per shoot with monthly total precipitation. D. hispida and E. gracilipes also showed a positive correlation among shoot length, monthly air temperature, and monthly precipitation.

Conclusions

Only 3 of the 15 studied species showed a correlation between shoot or foliage production and monthly climate variables during the wet growing season. Deciduous trees avoid foliage self-shading, producing slanting short shoots with leaf flush preceding heavy rains, facilitating rapid branch and foliage formation to offset the leaf-free period quickly. Conversely, evergreen trees, characterised by orthotropic long shoots and slower vegetative growth, rely on foliage self-shading to sustain leaf persistence during seasonal drought. Semideciduous species commonly exhibited shoot- and leaf-trait variables such as those observed, on average, in deciduous or evergreen trees, resulting in a continuous spectrum of trait variations among the leaf phenological groups.

Implications

Each growth strategy in every leaf habit showed a particular air space acquisition across seasons, usually keeping shoot and foliage production independent of monthly climate variability in the wet growing season. These findings emphasised the significance of characterising the leaf phenological assemblages of the vast Cerrado woody flora as inherent functional groups in a continuum of crown trait variation, enabling the identification of strategies to capture, use, and store resources in each tree group.